Hello :wave: Any suggestions on how to write a cus...

# serialization

[Dariusz Kuc]

Hello 👋
Any suggestions on how to write a custom KSerializer that behaves similar to the built-in ones for primitives? e.g. I can deserialize Double from Number (Int/Float) or String representation

var kotlinxDouble: Double = format.decodeFromString("""
    0
""".trimIndent())
println(kotlinxDouble)

kotlinxDouble = format.decodeFromString("""
    1.0
""".trimIndent())
println(kotlinxDouble)

kotlinxDouble = format.decodeFromString("""
    "2.0"
""".trimIndent())
println(kotlinxDouble)

tried

object BigDecimalStringSerializer : KSerializer<BigDecimal> {

    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("BigDecimal", PrimitiveKind.STRING)

    override fun serialize(encoder: Encoder, value: BigDecimal) {
        encoder.encodeString(value.toString())
    }

    override fun deserialize(decoder: Decoder): BigDecimal {
        val raw = decoder.decodeString() // <-- blows up when not a String representation, i.e. on 0 and 1.0 values from above
        return BigDecimal(raw)
    }
}

Is there something like decoder.getRawValue or something like that?

[Robert Jaros]

https://github.com/rjaros/kvision/blob/master/kvision-modules/kvision-common-remote/src/jvmMain/kotlin/io/kvision/types/Decimal.kt

[Robert Jaros]

Oh, you mean you want it to work with both 1 and "1"?

[Dariusz Kuc]

yeah

[Dariusz Kuc]

its part of a bigger problem that I'm trying to solve -> basically a field can be represented by any valid JSON primitive

[Dariusz Kuc]

the default behavior would be to read it as String

[Dariusz Kuc]

and then try to coerce it to some specific value type

[Dariusz Kuc]

in Jackson I can use @JsonCreator/@JsonValue to achieve this e.g. BigDecimal example (end users provide the conversion logic to/from JSON using converter)

data class BigDecimalWrapper(val value: BigDecimal) {
    @JsonValue
    fun rawValue() = converter.toJson(value) // can serialize to whatever format

    companion object {
        val converter: BigDecimalConverter = BigDecimalConverter()

        // can deserialize from Any
        @JsonCreator
        @JvmStatic
        fun create(rawValue: Any) = BigDecimalWrapper(converter.toScalar(rawValue))
    }
}

[Dominaezzz]

This should get you started.

object BigDecimalStringSerializer : KSerializer<BigDecimal> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("BigDecimal", PrimitiveKind.STRING)
    override fun serialize(encoder: Encoder, value: BigDecimal) {
        encoder.encodeString(value.toString())
    }
    override fun deserialize(decoder: Decoder): BigDecimal {
        val input = decoder as JsonDecoder
        val element = input.decodeJsonElement()
        val raw = element.jsonPrimitive.content
        return BigDecimal(raw)
    }
}

[Dariusz Kuc]

works like a charm, thanks @Dominaezzz